Minnesotaite

{{Short description|Phyllosilicate mineral in the pyrophyllite-talc group}} {{infobox mineral | name = Minnesotaite | boxwidth = | boxbgcolor = | image = Minnesotaite.jpg | imagesize = | alt = | caption = Minnesotaite | category = Phyllosilicate minerals | group = Pyrophyllite-Talc group | formula = (Fe²⁺,Mg)₃Si₄O₁₀(OH)₂ | IMAsymbol = Mns<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = | strunz = 9.EC.05 | dana = | system = Triclinic | class = Pinacoidal ({{overline|1}}) <br/><small>(same H-M symbol)</small> | symmetry = ''P''{{overline|1}} | unit cell = a = 5.623(2)&nbsp;Å, <br/>b = 9.419(2)&nbsp;Å, <br/>c = 9.624(3)&nbsp;Å; <br/>α = 85.21(3)°, β = 95.64(3)°, <br/>γ = 90.00°; Z&nbsp;=&nbsp;2 | color = Greenish gray to olive-green | colour = | habit = Occurs as microscopic needles or platelets, the needles occur in radiating clusters or in sheaves; also fibrous | twinning = Inferred based on X-ray patterns | cleavage = Perfect on {001}, micaceous | fracture = Uneven and irregular | tenacity = Brittle | mohs = 1.5 - 2 | luster = Greasy to waxy, dull | streak = | diaphaneity = Translucent | gravity = 3.01 | density = | polish = | opticalprop = Biaxial (-) | refractive = n_α = 1.578 - 1.583 n_β = 1.578 - 1.622 n_γ = 1.615 - 1.623 | birefringence = δ = 0.037 - 0.040 | pleochroism = X= pale green, Z= colorless to pale greenish yellow | 2V = Measured: 4° | dispersion = r < v moderate | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = <ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/minnesotaite.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-2722.html Minnesotaite on Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Minnesotaite.shtml Minnesotaite on Webmineral]</ref> }} '''Minnesotaite''' is an iron silicate mineral with formula: (Fe²⁺,Mg)₃Si₄O₁₀(OH)₂. It crystallizes in the triclinic crystal system and occurs as fine needles and platelets with other silicates.<ref name=HBM/> It is isostructural with the pyrophyllite-talc mineral group.<ref name=Mindat/>

==Occurrence== Minnesotaite was first described in 1944 for occurrences in the banded iron formations of northern Minnesota for which it was named. Co-type localities are in the Cuyuna North Range, Crow Wing County and the Mesabi Range in St. Louis County.<ref name=Mindat/><ref name=Gruner1>{{Cite book |last=Gruner |first=John |title=The Mineralogy and Geology of the Taconites and Iron Ores of the Mesabi Range, Minnesota |publisher=Office of the Commissioner of the Iron Range Resources and Rehabilitation |year=1946 |page=8,38}}</ref>

It occurs associated with quartz, siderite, stilpnomelane, greenalite and magnetite.<ref name=HBM/><ref name=Gruner>[http://www.minsocam.org/ammin/AM29/AM29_363.pdf Gruner, John W., ''The Composition and Structure of Minnesotaite, a Common Iron Silicate in Iron Formations,'' American Mineralogist, 1944, 29, 363-372]</ref> In addition to the low grade metamorphic banded iron formations it has also been reported as an alteration mineral associated with sulfide bearing veins.<ref name=Mindat/>

==References== {{Reflist}}

{{Authority control}} {{Phyllosilicates}}

Category:Triclinic minerals Category:Minerals in space group 2 Category:Pyrophyllite-Talc group